1. Field of the Invention
The present invention relates to semiconductor devices, and particularly to improvement in the structure for positioning semiconductor substrates and the structure for positioning parts for transmitting light signals functioning as trigger signals.
2. Description of the Background Art
FIG. 9 is a front sectional view showing an example of a pressure contact type thyristor of the light trigger type which is one of conventional pressure contact type semiconductor devices. As shown in FIG. 9, in this pressure contact type thyristor, a thermal compensating plate 3 formed of material having its coefficient of thermal expansion approximate to that of a semiconductor substrate 1 is attached to the lower main surface of the semiconductor substrate 1 having the thyristor elements built therein. This thermal compensating plate 3 and the semiconductor substrate 1 are soldered to each other with solder material such as aluminum or aluminum-silicon.
The thermal compensating plate 3 is subjected to the shaping processing at its end surface, and also subjected to the chemical treatment, and further, the surface treatment agent is applied thereto. A main electrode 5 formed of copper abuts on the lower main surface of the thermal compensating plate 3. This main electrode 5 is silver-soldered to an insulation tube 6 formed of ceramics through a metal plate 8.
Another thermal compensating plate 2 is provided on the upper main surface of the semiconductor substrate 1. This thermal compensating plate 2 is made to adhere to the upper main surface of the semiconductor substrate 1 with silicone rubber, for example. A main electrode 4 formed of copper abuts on the upper main surface of the thermal compensating plate 2. The main electrode 4 is silver-soldered to the insulation tube 6 formed of ceramics through a metal plate 7.
The insulation tube 6 establishes insulation between the two main electrodes and forms a housing accommodating the semiconductor substrate 1 and the like inside together with the main electrodes 4, 5 and the metal plates 7, 8. A metal tube 11a for guiding light signals and a metal tube 11b functioning as an exhaust spigot are attached to the insulation tube 6 by silver soldering.
A light guide 10 for guiding the light signals inputted from outside to a light receiving portion is inserted in the metal tube 11a. This light guide 10 airtightly adheres to the metal tube 11a with an adhesive agent such as solder or glass with low melting point. The light receiving portion 1a is provided at the center part of the semiconductor substrate 1, to which the light emitting end of the light guide 10 is fixedly coupled.
The light guide 10 and the light receiving portion 1a are bonded by using an optical coupling agent 21 such as silicone rubber or the like which has optical transparency, refractive index approximate to that of the light guide 10, and buffering effect. The light guide 10 is fixed to prevent a decrease of the coupling efficiency of the optical transmission system to transmit optical power as large as possible to the light receiving portion 1a.
The inside of the above-described housing is made airtight, and inert gas is sealed therein. With the semiconductor substrate 1, the thermal compensating plate 2, and the thermal compensating plate 3 accommodated in the housing, the end surface of the metal plate 8 silver-soldered to the main electrode 5 and the insulation tube 6 are finally welded, and the gas remaining inside is exhausted through the metal tube 11b and replaced by inert gas, and then the end portion of the metal tube 11b is arc-welded to realize the airtightness of the housing and seal of the inert gas.
The light signal is transmitted through an external optical fiber (not shown) from an external LED, LD, etc. (not shown), which serves as a light source, and then guided to the light entering end of the light guide 10 through an external connector (not shown). The light guide 10 changes the direction of progress of the incident light signal by 90.degree. and irradiates the light receiving portion 1a from the light emitting end facing to the light receiving portion 1a of the semiconductor substrate 1.
The semiconductor substrate 1 converts the light signal into the photoelectric current in the vicinity of the light receiving portion 1a and amplifies the photoelectric current to establish a conductive state between the two main electrodes 4 and 5. That is to say, this device performs switching operation triggered by the light signals.
FIG. 10 is a front sectional view of another conventional pressure contact type thyristor disclosed in Japanese Patent Laying-Open No. 4-120772. This device is a GTO (Gate Turn Off) thyristor of the electric trigger type having the so-called alloy-free structure, in which the semiconductor substrate 1 and the thermal compensating plates 2 and 3 are not soldered.
This device is different from the device shown in FIG. 9 in that the semiconductor substrate 1 and the thermal compensating plates 2, 3 are not soldered, so that heat distortion resulted from difference in coefficients of thermal expansion among them, i.e., the warp transformation caused by the temperature change is suppressed to about several .mu.m. Accordingly, as uniform pressure welding is realized between the thermal compensating plates 2, 3 and the main electrodes 4, 5, it is advantageous in that the thermal and electric contact resistances are low in the pressure contact.
In FIG. 10, the same characters are allotted to the same parts as those in the device shown in FIG. 9, and detailed descriptions thereof are not repeated. In the device shown in FIG. 10, the semiconductor substrate 1 is subjected to the shaping processing at its end surface, and then to the chemical treatment, and further, the surface treatment agent is applied thereto. Stepping processing is applied to the end surface of the thermal compensating plate 3, and the semiconductor substrate 1 is made to adhere to the step portion with silicone rubber 23 or the like. The adhesion is made only at the end, so that thermal distortion does not occur in the thermal compensating plate 3 as described above.
Furthermore, similarly to the device of FIG. 9, the main electrode 4, the metal plate 7 and the metal tube 11 are silver-soldered to the insulation tube 6 formed of ceramics to form a housing. A groove is formed in the center portion of the bottom of the main electrode 4 abutting on the thermal compensating plate 2, in which groove a guide ring 50 formed of an insulating material is inserted. An output end of a gate lead line 60 transmitting the electric trigger signals is incorporated in this guide ring 50, and its one input end passes through the metal tube 11.
The guide ring 50 presses and energizes the output end of the gate lead line 60 against the upper main surface of the semiconductor substrate 1 with the elastic force of a spring 31. The portion between the input end and the output end of the gate lead line 60 is covered with an insulating tube 61. The insulating tube 61 prevents electric contact of the gate lead line 60 with the main electrode 4.
Similarly to the device of FIG. 9, the housing is made airtight inside and inert gas is sealed therein. With the semiconductor substrate 1, the thermal compensating plate 2 and the thermal compensating plate 3 accommodated in the housing, the end surface of the metal plate 8 silver-soldered to the main electrode 5 and the insulation tube 6 are welded at last, and the gas remaining inside is exhausted through the metal tube 11 and replaced by the inert gas, and then the end of the metal tube 11 is arc-welded to realize the airtightness of the housing and sealing of the inert gas.
As the conventional semiconductor devices are configured as discussed above, they have such problems as listed below.
First, as the semiconductor substrate 1 and the thermal compensating plate 3 are bonded by means of the solder material in the conventional pressure contact type semiconductor device, it has been a problem that warp transformation is caused in the coupled body of the semiconductor substrate 1 and the thermal compensating plate 3 by the difference in thermal shrinkage resulted from the difference in the thermal expansion coefficients of the two when they are cooled after the alloy process, resulting in uneven contact surfaces between the semiconductor substrate 1 and the main electrodes 4, 5 to decrease the yield of the device. Particularly, with the recent increase of calibers of the devices, this problem is becoming more serious.
As a countermeasure, such devices as have the alloy-free structure in which the semiconductor substrate 1 and the thermal compensating plate 3 are not alloyed as described above are appearing. However, this conventional device of the alloy-free type involves a problem that the semiconductor substrate 1 and the thermal compensating plate 3 move in the radial direction or in the axial direction when assembled or transported because they are not fixed and cause damage or the semiconductor substrate 1. Particularly, the devices of the optical trigger type involve the problem that the light guide 10 may be damaged, or the relative position of the light receiving portion 1a of the semiconductor substrate 1 and the light emitting end of the light guide 10 may be displaced, so that the light signals are not transmitted to the semiconductor substrate 1, with the result that the device does not operate adequately.
Second, in the conventional light trigger semiconductor device, the loss heat generated in the semiconductor substrate 1 by the passage of current is transmitted to outside through the thermal compensating plates 2, 3 and the electrodes 4, 5 to prevent the semiconductor substrate 1 from being overheated. However, a notch 4a is formed in the main electrode 4 to introduce the light guide 10 for transmitting the light signals, and a groove with certain volume is formed in the center portion of the bottom of the main electrode 4 when a guide ring or the like is used for normally positioning the output end of the light guide 10 to the light receiving portion 1a of the semiconductor substrate 1. The conventional device has a problem that the transmission efficiency of the loss heat decreases more as the volume of the notch 4a and the groove becomes larger.
Third, when assembling the conventional light trigger semiconductor device, the light guide 10 is introduced, and then, welding is performed between the metal plate 7 previously fixed to the periphery of the main electrode 4 and the insulation tube 6 to fixedly join the main electrode 4 to the insulation tube 6. Accordingly, it has been a problem that the main electrode 4 turns when temporarily assembled in the process before the welding is finished and the notch 4a touches the light guide 10 to give damage to the light guide 10.
Fourth, as both the light entering end and the light emitting end of the light guide 10 are fixed in the conventional light trigger semiconductor device, there is a possibility of damaging the light guide 10 by the expansion and shrinkage of parts caused by repeated temperature change. In addition, it is a problem that the yield of the device decreases in the process of incorporating the light guide 10 into the device, i.e., in the process of adhesion using solder and realizing the airtight state.
Fifth, as the conventional pressure contact type semiconductor device of the alloy-free structure is constructed as shown in FIG. 10, the end of the semiconductor substrate 1 must be stuck to the thermal compensating plate 3 so that the semiconductor substrate 1 and the thermal compensating plate 3 will not slip off from the predetermined relative position, and this process is not easy. Furthermore, as the silicone rubber or the like used for adhesion has fluidity, it may flow in between the semiconductor substrate 1 and the thermal compensating plate 3.